Add an ssh check periodic task

If we can't ssh into a node, delete it.

Change-Id: Ie53187ff5c37941709a2cb708b0bf76116138093
Change credentials-id parameter in config file

To use a dash to be consistent.

Change-Id: Ifee3cfe9ad18989d09ef896408e7bb3f78e54f2c
Reduce timeout when waiting for server deletion

From 1 hour to 10 minutes.  If it isn't deleted, it will get
deleted by the next pass of the cleanup process.

Change-Id: I6dd1693d14fd215117ddbed8440ff4abe02c374c
Move setup scripts destination

Move them to /opt/nodepool-scripts so they are in a nice
world-readable location so that they can be run as any user.

Change-Id: I007e341fbe17067c164d3712fcfb7e744bdd80e9